1. Field of the Invention
The present invention relates to an organic light emitting display device, which includes a photo diode for receiving light of red wavelength incident from an external source to a non-pixel region, and for controlling brightness of an organic light emitting device.
2. Discussion of Related Art
In general, an organic light emitting device includes: a pair of electrodes having an anode electrode and a cathode electrode, and a light emitting layer. In more detail, the organic light emitting device can include: a hole injecting layer, a hole transporting layer, an electron injecting layer and an electron transporting layer. Such an organic light emitting device can emit light because of the following light emitting principle. Positive charge carries or holes are injected into a hole injecting layer from an anode electrode, and the holes injected into the hole injecting layer are transported to a light emitting layer by a hole transporting layer. Further, negative charge carriers or electrons are injected into an electron injecting layer from a cathode electrode, and the electrons injected from the electron injecting layer are transported to the light emitting layer by an electron transporting layer. The holes and the electrons that are transported to the light emitting layer are then coupled with each other to form excitons, thereby light-emitting the light emitting layer.
Hereinafter, a conventional organic light emitting device will be described in more detail with reference FIG. 1.
FIG. 1 is a cross-sectional view of a conventional organic light emitting diode.
Referring to FIG. 1, an organic light emitting diode 10 includes a buffer layer 110 on a substrate 100. A thin film transistor 120 is formed over the buffer layer 110. The thin film transistor 120 includes: a semiconductor layer 121, a gate electrode 122, and source and drain electrodes 123. A planarization layer 130 is formed over the thin film transistor 120, a first electrode layer 140 electrically connected with the source or drain electrode 123 is formed over the planarization layer 130, and a pixel defined layer 150 is formed over the first electrode layer 140. The pixel defined layer 150 includes an opening part for at least partially exposing the first electrode layer 140. A light emitting layer 160 is formed over the opening part. A second electrode layer 170 is formed over the light emitting layer 160. Besides, one or more of an electron injecting layer, an electron transporting layer, a hole transporting layer and a hole injecting layer can be formed between the first electrode layer 140 and the second electrode layer 170.
In the above organic light emitting diode, the organic material, which is the light emitting layer 160 of the organic light emitting diode, may be deteriorated to change the brightness of pixel, as time passes, resulting in that the image quality or brightness of a display is displayed in values different from the expected values. Accordingly, the organic light emitting diode does not have a long lifespan.
In order to solve the above problems, an approach of forming a photo diode in the organic light emitting diode is proposed. This approach allows for a constant brightness to be represented for an input signal regardless of the deterioration of the organic light emitting device by using the photo diode to convert light energy received by (or incident on) the photo diode into an electric signal.
However, the aforesaid photo diode has a relatively low light receiving rate (less than 50% according to a wavelength of light), and there is a limit to its control of the brightness of the organic light emitting device.